Vacuum-tube manufacture



Dec. 15, 1925- M. J. KELLY VACUUM TUBE MANUFACTURE Filed June 30, 1921 Patented A Dec. 15, 1925.

UNITED STATES MERVIN J. KELLY. OF NEW YORK, N- Y., ASSIGNOB '10 WESTERN ELECTRIC COMPANY,

INCQBPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

VACUUM-TUBE manurncruan.

Application filed June 30,1921. Serial No. 481,610.

To all whom it may concern: Be it known that I, MERVIN J. KELLY, a citizen of the United States of America, residing at New York, in thecounty of New York, State of New York, have invented certain new and useful Improvements in Vacuum-Tube Manufacture, of which the following is a full, clear, concise, and exact description. a

This invention relates to induction furnaces and more especially to their use in the manufacture of vacuum tubes for denuding the electrodes of occluded gases during the exhaust of the tubes.

An object of this invention is to heat the vacuum tube electrodes by supplying electrical energy to them inductively.

According to the invention high frequency oscillations are supplied to an induction coil within which is arranged a vacuum tube having electrodes to be heated. The oscillations supplied to the coil generate an electromagnetic field within the coil which induces eddy currents in the electrodes to heat them. As the eddy currents produced are proportional to a power of 4 the frequency greater than the first, it is desirable that the frequency be of a very high order. Preferably an audion oscillator is used as a source of oscillation as frequencies of the order of 500,000 cycles may be readily obtained from such a source. When used in connection with-vacuum tubes having cylindrical anodes, such a device is extremely effective in heating the electrodes as it is possible to obtain a very close coupling between the coil and the electrode by arranging the electrodes coaxial of the coil.

This invention will be better understood by having reference to the following specification and accompanying drawing wherein is disclosedsoniewhat diagrammatically an apparatus for producing the electromagnetic field and is illustrative of the method of heating the anode thereby.

The vacuum tubes 1 to be exhausted are connected to a vacuum pump (not shown) by means of the glass tubing 2. Arranged within'the vacuum tubes are the anodes'3 which are to be denuded of their occluded gases. The anodes are heated to the desired temperature by means of an induction furnace which comprises the coils I and I. These coils together with the variable condensers 11 and 12 comprise an oscillation circuit. The frequency of oscillations generated in this circuit is dependent upon the sum of the capacity reactance of the condensers 11 and 12 and upon the inductive reactance of the coils I and I.

As a means for supplying exciting current to the oscillation circuit, there is provided an electron dlscharge oscillator which comprises a vacuum tube V having the cathode F, the control electrode 0 and the anode A, the input and output circuits of the tube being connected with the oscillation circuit between the coils I and I and the variable condensers 11 and 12 respec tively. Included in the output circuit of the oscillator is a generator G and a high frequency choke coil 13. In the input circuit of the-oscillator is provided a small resistance 14 to prevent high frequency singing in said circuit, and a grid leak resistance 15 in combination with a condenser 16 maintains the average grid potential. The connections of the input and output circuits of the oscillator to the oscillation circuit comprises stopping condensers 17 to prevent direct current flowing into the oscillation circuit, The cathode of the vacuum tube V is grounded at18 to protect both the input and output circuits of the oscillator against any accidental grounding of either of the circuits. cathode F by the battery 19.

This arrangement is capable of generating, in the oscillation circuit, oscillations of the order of five hundred thousand cycles which has been found to be the frequency at Which the desired eddy currents are obtainable with the minimum expenditure of energy from the generator G. These oscillations produce the high frequency field which induces in the anode of the tube to be exhausted the eddy currents by means of which the anodes are heated.

In order to providea close coupling between the anodes 3 ofthe tubes to be exhausted and the coils I and I the tubes are Heating current is supplied to the inserted in the coils and the anodes are made During the exhaustion of the tubes the high frequency current is supplied to the coils I and 1' thereby producing an electromagnetic field paralle I anodes. There are, therefore, induced in the anodes Foucault currents which, be-

cause of the tubular configuration of the anodes, have circumferentially complete paths and which generate in the anode sufficient heat to drive out therefrom any occluded. gas. Because. of the extremely high frequency of the current supplled to the induction coils and because of the close coupling between the coils and the anodes due to the configuration of the anodes and their position in the coils this arrangement is highly efiicient and the necessary temperature can be obtained by the expenditure oii a comparatively small amount of electrical energy.

The temperature to which the electrodes are heated can be controlled by varying the high frequency current in the oscillationcircuit. This can be done by varying the alternating potentials across the input and output circuits by varying the capacities 11 and 12; or it may be done by varying the potential of the generator G.

Although this apparatus is disclosed as being adapted for heating the anodes of vacuum tubes, it may be used for heating any metal.

What is claimed is:

1. A method of exhausting a vacuum tube having an anode by the use of a thermionic oscillator having an inductive element which comprises surrounding said vacuum tube by said inductive element and producing a high frequency electromagnetic field in said inductive element to directly heat the anode of said vacuum tube.

2. A method of exhaustin a vacuum tube havinga cylindrical anode by the use of a to the axes of thehigh frequency thermionic oscillator having an inductive element serving as an induction heater, which comprises producing a high frequency alternating current by said oscillator in said inductive element, and heating the anode of said tube by subjecting it to the electromagnetic field produced in said inductive element with the axis of the anode parallel tothe lines of force of the field.

3. In combination, a thermionic oscillator comprising an induction coil for producing an electromagnetic field, and a vacuum tube having an anode arranged within said coil whereby the electromagnetic field is effective to produce eddy currents in said anode.

4. In combination, a source of electrical energy, a vacuum tube having its output circuit connected with its input; circuit whereby a portion of the energy of the output circuit is fed back into said input circuit, an induction coil having its terminals connected with the control electrode and anode of said vacuum tube, and a vacuum tube having an anode arranged Within said coil whereby current supplied to said induction coil is effective to produce eddy currents in said anode.

5. Apparatus for exhausting a vacuum tube having a cylindrical anode comprising a thermionic oscillator for supplying high frequency alternating current, and an in ductive coil forming a part of said oscillator and arranged to receive said tube with the axes of the anode and the coil coincident.

6. An oscillator having capacity reactance and inductance reactance for determining the frequency generated, said inductive reactance comprising a coil, a vacuum tube within said coil having an electrode adapted to be heated by the eddy currents pro- 

